1. Field of the Invention
The present invention relates to an image forming apparatus that can correct a condition for forming an image, and a correction method of an image forming condition.
2. Description of the Related Art
There has been known a color image forming apparatus that forms images of a plurality of color components, superimposes these images, and outputs the resultant image. In a color image forming apparatus described above, it is important, in order to obtain an excellent image quality, to form images of the respective color components under a predetermined condition. For example, a positional deviation (color misregistration) upon superimposing images of the respective color components corresponds to the image quality. Alternatively, keeping the density of each image of each color component to be a predetermined density corresponds to the image quality. Color misregistration is inherent to a color image. A great color misregistration might be evaluated as a poor image quality. When there is unevenness in the density of each color component, a sense of congruity occurs in a hue. In order to keep the image quality to be in a predetermined state, a technique has been performed in which a pattern is formed after a lapse of predetermined time, and this pattern is read to detect a misregistration amount from a reference for correcting a condition for forming an image. In order to make the misregistration amount small, it is preferable that the correction for the misregistration amount is carried out in a short interval. However, it takes much time to detect the misregistration amount, since the misregistration amount is detected by forming a pattern. Further, toner or ink, which is used to form an image, is consumed for forming a pattern. Even if a consumption amount of toner is small in one correction, the consumption amount reaches a non-negligible amount when the correction of the misregistration amount is frequently repeated. In the case of a user who mostly forms a monochrome image, for example, a color toner or the like is consumed although he/she rarely forms a color image. This situation is unreasonable. In particular, cost for a color toner is more expensive than the cost for a black toner used for monochrome image formation in most cases. A problem of who is to pay the toner expense used for the pattern formation is likely to arise.
As one technique for reducing the unreasonableness described above, a technique has been proposed in which a preliminary check is executed for confirming a degree of color misregistration, when the time for correcting color misregistration has come, and when the color misregistration is great, the correction described above is executed (e.g., see Japanese Unexamined Patent Application No. 2005-202110)
As described above, a technique for shortening a time taken for the correction of the image quality has conventionally been discussed. On the other hand, a demand for the image quality of a color image has more and more increased. The detection of the misregistration amount and the correction are inevitable. A technique capable of reducing a processing time taken for the correction and a consumption amount of toner or the like without reducing a frequency for performing a correction of a misregistration amount has been demanded.
On the other hand, a color image forming apparatus generally forms a color image by using four color components of yellow, magenta, cyan, and black. Some apparatuses provide an extended color reproduction area or satisfactory halftone capability with the use of more color components. In either case, a pattern should be formed for each color component so as to detect the misregistration amount from a reference, in order to correct an image quality.
Considering the consumption amount of each color component, the toners exclusively used for a color image formation, such as yellow, magenta, cyan, or the like, tend to be consumed uniformly compared to a black toner used also for a monochrome image formation. It is found from a commercial distribution manner of a color toner that each of the colors is frequently available as one set. However, since the composition ratio of each color component is different depending upon an image, the consumption amount is not always the same. Even so, if any one of the colors of the color components is consumed, the color image formation cannot help being inhibited. From this viewpoint, toners exclusively used for the color image formation are preferably consumed equally.